Some of the major goals of high speed packet access (HSPA) evolution include higher data rates, higher system capacity and coverage, enhanced support for packet services, reduced latency, reduced operator costs and backward compatibility. Meeting these goals requires evolutions to the radio interface protocol and network architecture. More specifically, meeting these goals has required a set of enhancements and architecture changes to layer 2 (L2), (i.e., radio link control (RLC) and medium access control (MAC)), functionalities.
Some of the L2 enhancements include flexible size RLC protocol data units (PDUs), (i.e., RLC PDUs having flexible sizes), high speed MAC (MAC-hs) segmentation/concatenation and multiplexing. In universal terrestrial radio access (UTRA) Release 6 (R6), the acknowledge mode (AM) RLC entities can only use fixed size RLC PDUs, (i.e., RLC PDUs having a fixed size). In addition, the MAC-hs sub-layer in the Node-B can only support concatenation of dedicated MAC (MAC-d) PDUs. The L2 enhancements of UTRA Release 7 (R7) result in significant RLC/MAC changes of R6 features.
Currently, when radio bearers (RBs) are setup or reconfigured via radio resource control (RRC) signaling, the information element (IE) “RB mapping info” is present. The “RB mapping info” contains information about the RLC instance and transport channels corresponding to the RB.
The MAC-hs configuration has to be the same across all RBs mapped to a high speed-downlink shared channel (HS-DSCH), or else an invalid configuration will result.
In HSPA, the high speed shared channels are monitored by a wireless transmit/receive unit (WTRU) in a single cell, (i.e., the serving HS-DSCH cell). Due to mobility, when the WTRU is moving from one cell to the other, the WTRU needs to perform a serving cell change by switching to a new serving HS-DSCH cell and terminating communication with the old serving HS-DSCH cell. In a Node-B relocation procedure, an inter-Node-B handover occurs from an old Node-B, (i.e., a source Node-B) to a new Node-B, (i.e., a target Node-B).
At the time of a serving Node-B change, the target Node-B needs to start transmission of data over the new configuration. The handover can occur among evolved HSPA Node-Bs which support the L2 enhancements, or to/from cells with or without L2 enhancements. For both cases, the WTRU must be able to perform a handover, adjust to the new configurations, and minimize data loss.
With the introduction of new L2 enhancements, new procedures need to be defined in order to optimize and minimize data loss during a handover between R7 cells, or between an R7 cell and an R6 cell. Specifically, procedures that deal with resetting of the MAC-hs entity need to be modified in order to account for the new L2 enhancements.
In addition, it cannot be assumed that all of the R6 Node-Bs will be upgraded at the same time to R7 Node-Bs. Therefore, handovers between R6 and R7 cells may frequently occur. Due to the functional changes of the RLC and MAC, methods to perform handovers with minimal loss of quality and data between these cells must be defined. Specifically, on the WTRU side, the MAC-hs and the RLC must perform functional changes during the handovers.